Method of forming a cam-engaged rocker arm

ABSTRACT

A method and system for forming a cam engaged rocker arm includes a stamping process where metal is forced into die cavities to build up material in a desired area of a blank to create an intermediate article. The blank is further formed by a shaving process where the built-up material and additional material is formed into a valve guide for the rocker arm.

This application claims the benefit of Provisional Application60/498,076, filed on Aug. 27, 2003, the contents of which are herebyincorporated herein in their entirety.

TECHNICAL FIELD

The present invention relates to a method of forming a rocker armincluding a valve guide. In particular, the invention relates to using astamping die having a pair of cavities to form the valve guides of therocker arm.

BACKGROUND OF THE INVENTION

In automotive and other applications, an overhead cam engine typicallyutilizes a plurality of cam engaged rocker arms to open valves. Theserocker arms pivot at one end, contact the valve at an opposite end, andsupport a roller between the two ends. The roller engages the cam andthe cam rotates to move the roller, thereby causing the rocker arm topivot at a pivot end, and push the valve.

Rocker arms can be manufactured by casting metals, blanking and forming,ceramic molding, and other methods. Stamping a metal blank to form acam-engaged rocker arm including a valve stem guide is common in theart. The valve stem guides of the rocker arms are typically formed usinga punch and cavity, folding or coining process. During the coiningprocess, an upper die and a lower die punch an area of the metal blankto plastically deform the metal blank. Generally, the area of the metalblank being coined has a thickness greater than the remaining metalblank, thereby providing additional material to use in forming the valveguides. FIG. 1 illustrates a typical metal blank 8 used in themanufacture of a cam-engaged rocker arm. The metal blank 8 illustratedis of uniform thickness and is folded by turning up two opposing edges,and valve guides are formed by plastically deforming material to thedesired locations. This plastic deformation typically moves materialfrom nearby areas of the blank to build up a valve guide. In thisforming operation, the thickness of the blank area that lost materialmay be below a desired minimum thickness. A desired minimum thicknessfor a rocker arm must be maintained for purposes of strength anddurability after a surface hardening treatment even if some of thematerial of the blank is used to form valve guides.

One drawback to this method is the extreme difficulty in providing ablank with sufficient thickness in a desired area for forming the valveguides without making a remaining portion of the rocker arm too thin ina later forming operation. In practice, it has been found to be nearlyimpossible to balance these competing needs.

SUMMARY OF THE INVENTION

The present invention overcomes the deficiencies of the prior art bypreparing a blank of generally uniform thickness for forming the valveguides of a rocker arm. In one embodiment, a method and system forforming a cam-engaged rocker includes a stamping process where metal isforced into die cavities to build up material in a desired area of ablank to create an intermediate article. The intermediate article isfurther formed by a shaving process where the built-up material andadditional material is formed into a pair of valve guides for the rockerarm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a prior art metal blank used for forming acam-engaged rocker arm.

FIG. 2 is a perspective view of a cam engaged rocker arm formed inaccordance with an embodiment of the present invention.

FIG. 3 is a sectional side view of the rocker arm of FIG. 1.

FIG. 4 is a top view of a metal blank before forming a cam-engagedrocker arm according to an embodiment of the present invention.

FIG. 5 is a top view of an intermediate article after undergoing a firststamping process according to an embodiment of the present invention.

FIG. 6 is a perspective view of a further intermediate article accordingto an embodiment of the present invention, after undergoing a furtherstamping operation to form side walls.

FIG. 7 is a front view of the further intermediate article of FIG. 6illustrating the die used for pinch forming valve guides according to anembodiment of the present invention.

FIG. 8 is a front view similar to FIG. 7, but illustrating the die afterpinch forming the valve guides.

FIG. 9 is a top view of an alternate embodiment of the metal blank ofFIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 2 and 3, a rocker arm 10 is illustrated to include ametal body 12, a valve end 14, a pivot end 16, sidewalls 18, a centralportion 20 located between the valve end 14 and the pivot end 16, and abridge, or cross member, 22 extending between sidewalls 18. Metal body12 is defined by an upper surface 24, a lower surface 26, and an outerperipheral surface 28. As illustrated, central portion 20 has a centralaperture 30 and roller apertures 32 formed therein. Central aperture 30is defined by an inner surface 34. Roller apertures 32 are defined byroller aperture surfaces 36. Valve end 14 includes valve guides 40extending from lower surface 26. Each valve guide 40 is defined, atleast in part, by an inboard surface 42, an outboard surface 44, and adistal surface 46. A pair of shaved areas, S, are illustrated on lowersurface 26, intersecting outboard surfaces 44. Valve guides 40 areillustrated to have a height H, measured perpendicular to lower surface26, between distal surface 46 and lower surface 26. As best seen in FIG.3, inboard surfaces 42 are separated by a distance D. With continuedreference to FIGS. 2 and 3, the pivot end 16 includes a cup 50 formedtherein and adapted to rotate on a pivot (not shown).

Referring now to FIG. 4, a metal blank 110 is shown according to anembodiment of the present invention. As illustrated, metal blank 110 hasa valve end 114, a pivot end 116, and a central portion 120 locatedbetween the valve end 114 and the pivot end 116. The metal blank 110 hasan upper surface 124, a lower surface 126, and an outer surface 128.Upper surface 124 and lower surface 126, as illustrated, are preferablyidentical in outline. The metal blank 110 has a substantially uniformcross-sectional thickness T as measured between the upper surface 124and the lower surface 126. The metal blank 110 includes an additionalmaterial volume, forming ears 140, about the valve end 114. The ears 140include the volume circumscribed by a Line L, the outer surface 128,upper surface 124, and lower surface 126, adjacent valve end 114, anddefine an outboard portion 160 of the metal blank 110. Metal blank 110is segmented into zones A, B, C, D, E, F, and G, each having a thicknessT, as discussed below.

FIG. 5 illustrates an intermediate article 210. As illustrated, metalintermediate article 210 has a valve end 214, a pivot end 216, and acentral portion 220 located between the valve end 214 and the pivot end216. The intermediate article 210 has an upper surface 224, a lowersurface 226, and an outer surface 228. The intermediate article 210 hasa substantially uniform cross-sectional thickness T as measured betweenthe upper surface 224 and the lower surface 226. Intermediate article210 is shown to include projections 240 defined, at least in part, by aninboard surface 242, an outboard surface 244, and a distal surface 246.As illustrated, inboard surfaces 242 are separated by a distance W.Intermediate article 210 is segmented into zones A, B, C, D, E, H, andI. Zones A, B, C, D, E, and H, each have a thickness T substantiallyequal to the thickness of metal blank 110. Zone I differs from Zone G inthat Zone I has projections 240 and Zone G has ears 140. Peripheralsurface 228, viewed along the Z-axis, closely approximates the outlineof the metal blank 110 without ears 140, as defined by peripheralsurface 128 and Lines L. Thus provided, the metal blank 110 of FIG. 4can be formed into the intermediate article 210 of FIG. 5, as describedbelow. As illustrated, Zones A, B, C, D, and E of metal blank 110 andintermediate article 210 are substantially identical. Zone G containsears 140 that are plastically deformed, by a Force P and resulting ForceP′ (FIG. 4), inward toward each other to produce a resulting Zone I.Zones F and H are preferably identical, although Zone H may be slightlydistorted with respect to Zone F as a result of the forming operationdescribed herein.

With reference to FIG. 6, a further formed intermediate article 310 inthe manufacture of rocker arm 10 is illustrated to include a valve end314, a pivot end 316, and a central portion 320 located between thevalve end 314 and the pivot end 316. The further formed intermediatearticle 310 has an upper surface 324, a lower surface 326, and an outersurface 328. The further formed intermediate article 310 has asubstantially uniform cross-sectional thickness T as measured betweenthe upper surface 324 and the lower surface 326. Preferably, thickness Tdoes not vary between rocker arm 10, metal blank 110, intermediatearticle 210, and further formed intermediate article 310. Further formedintermediate article 310 is shown to include sidewalls 318, a crossmember 322, and projections 340 defined, at least in part, by an inboardsurface 342, an outboard surface 344, and a distal surface 346. Asillustrated, inboard surfaces 342 are separated by a Distance X.Preferably, Distance X is substantially equal to Distance W, although aslight variation between these distances caused by the formingoperations described herein may be experienced. In the embodimentillustrated, sidewalls 318 are about identical in outline to sidewalls18.

Referring now to FIGS. 7 and 8, an embodiment of a stamping die 400 forforming valve guides 40 is illustrated to include a center post 402, apair of cams 404 having a shaving edge 410. Center post 402 isillustrated to include a valve guide forming surface 414. Shaving edge410 is preferably curved to match the curve of the intersecting linebetween valve guide 40 and lower surface 26, as best seen in FIG. 3. Asillustrated in FIG. 6, stamping die 400 has a further formedintermediate article 310 positioned therein and prepared for a shavingoperation to create valve guides 40. As illustrated in FIG. 8, stampingdie 400 has one rocker arm 10 positioned therein after the shavingoperation has formed valve guides 40.

An embodiment of the method of forming the rocker arm 10 from metalblank 110 will now be described. The metal blank 110 undergoes a firststamping process in which a stamping die (not shown), having a pair ofcavities (not shown) which are used to form the projections 240 ofintermediate article 210. The cavities of the stamping die are centrallylocated about the valve end 14 of the metal blank 110. The metal blank110 is stamped such that during the stamping process, the ears 140 fromthe outboard portion 160 of the metal blank 110 are forced inward towardthe cavities of the stamping die, thereby displacing material adjacentlower surface 126 into the cavities to form projections 240 (FIG. 5).Projections 240 are formed by drawing the ears 140 from the outboardportion 160 while minimizing any change to the cross-sectional thicknessof the intermediate article 210 that does not include projections 240.The ears 140 are driven inward, plastically deforming material of metalblank 110 into the pair of cavities of the stamping die, producingprojections 240. Preferably, each ear 140 produces a projection 240during this forming operation. Thus formed, intermediate article 210 hasan identical outline defined by outer surface 228 as outer surface 128of metal blank 110 with the exclusion of the ears 140. Thus, thematerial volume of ears 140 is about equal to the material volume of theprojections 240.

At the completion of this stamping step, projections 240 are positionedwithin the cavities due to the plastic flow of material from metal blank110. FIG. 5 best illustrates the intermediate article 210 after thefirst stamping process has been completed.

A further processing step of the method presented herein involves theforming of sidewalls 18. In this step, the intermediate article 210 ofFIG. 5 is formed into the further formed intermediate article 310 ofFIG. 6 by a folding operation. This folding operation forms sidewalls318 by folding the sides of further formed intermediate article 310about 90° toward upper surface 324 along the length of further formedintermediate article 310 from valve end 314 to pivot end 316.

As illustrated in FIG. 7, the further formed intermediate article 310 ofFIG. 6 undergoes a shaving process to form valve guides 40. The shavingprocess is performed by pinching material between upper surface 324 andlower surface 326 between the cams 404 and shaving the material towardthe center post 402. As the material is shaved, the material isplastically deformed toward projections 340, plastically deforming thematerial of projections 340, until both volumes of material are formedinto each valve guide 40. This shaving process creates a shaved area S(FIGS. 2 and 8), that is defined by the material of lower surface 26that was exposed by the shaving process. As best seen in FIG. 7,distance X, between projections 340 of further formed intermediatearticle 310 is greater than the width of center post 402 adjacent lowersurface 326. In this manner, further formed intermediate article 310 canbe positioned within die 400 without having to force further formedintermediate article 310 into position. In an alternate embodiment,inboard surfaces 342 may be angled such that their orientation towardlower surface 326 is less than 90°, and the distance between distalsurfaces 346 is greater than the minimum distance between projections340, thereby eliminating any difficulty of interfering surfaces whenpositioning further formed intermediate article within die 400.

The shaving process results in a minimum of approximately 65% of stockthickness being maintained across the shaved area A so as not to createa through harden heat treat condition in the shaved area. The stockthickness is the original thickness of metal blank 110 as measured fromupper surface 24 to lower surface 26. This stock thickness is preferablyabout 3 mm (0.12 inch) to about 3.94 mm (0.16 inch). It is desired tomaintain a minimum thickness of the resulting rocker arm in the shavedarea A, as measured between the shaved area A and the upper surface 24.The minimum required thickness for rocker arm 10 adjacent shaved area Ais determined by the depth of hardening experienced by rocker arm 10 ina post-forming hardening treatment and the desired soft core thickness.A rocker arm with a hardened surface and soft core is typically desiredfor purposes of durability and wear resistance. In the embodiment shown,the post forming hardening treatment will harden the rocker arm 10 to amaximum depth of about 0.020 inches measured from all surfaces.

FIG. 9 illustrates a metal blank 510 as an alternate embodiment of themetal blank 110. As illustrated, metal blank 510 has a valve end 514, apivot end 516, and a central portion 520 located between the valve end514 and the pivot end 516. The metal blank 510 has an upper surface 524,a lower surface 526, and an outer surface 528. Upper surface 524 andlower surface 526, as illustrated, are preferably identical in outline.The metal blank 510 has a substantially uniform cross-sectionalthickness T as measured between the upper surface 524 and the lowersurface 526. The metal blank 510 includes an additional material volume,forming ears 540, about the valve end 514. The ears 540 include thevolume circumscribed by a Line M, the outer surface 528, upper surface524, and lower surface 526, adjacent valve end 514, and define anoutboard portion 560 of the metal blank 510. Metal blank 510 issegmented into zones A, B, C, D, E, J, and K, each having a thickness T.

Metal blank 510 is formed into intermediate article 210 by forcing ears540 into the valve end 514 as metal plastically flows into the cavitiesforming projections 240, as discussed herein. Preferably, each ear 540produces a projection 240 on Zone K at valve end 514 during this formingoperation.

Cup 50 and central aperture 30 may be formed in lower surface 26 at anyappropriate time when processing metal blank 110 into the rocker arm 10.As presently preferred, central aperture 30 is formed and cup 50 isformed as the last forming step, after pinch forming of valve guides 40.Roller apertures 32 may be formed either by machining or in-diepiercing. Preferably, roller apertures 32 are formed after pinch formingvalve guides 40. Outer curved, or peripheral, surfaces 28, 128, 228, or528 may be completely curved, have straight portions, or includestraight portions intersecting at predetermined angles.

While the invention has been described with respect to specific examplesincluding preferred modes of carrying out the invention, those skilledin the art will appreciate that there are numerous variations andpermutations of the above described systems and techniques that fallwithin the spirit and scope of the invention as set forth in theappended claims. For example, while valve guides are illustrated,another form of the guides may also be useful at the pivot end.

1. A method of manufacturing a cam-engaged rocker comprising: obtaininga metal blank, the blank defined, at least in part, by two opposingsurfaces and an outer peripheral surface, the blank having a generallyuniform thickness as measured between the two opposing surfaces, whereinthe two opposing surfaces each generally lie within a defined plane, theblank further having a valve end, a pivot end, and at least one earadjacent one of the ends, wherein the ear defines a predeterminedportion of the metal blank extending between the two opposing surfaces,and the outer peripheral surface defines, in part, an outline of theear; and stamping the metal blank using a stamping die having a cavityto produce an intermediate article, wherein the stamping die ispositioned adjacent the metal blank such that the cavity is adjacent oneof the two opposing surfaces at the valve end, and the cavityselectively permits a portion of the blank to increase in thickness asthe blank is stamped, such that the ear is pressed inward into the endand a projection is formed by the flow of a portion of the metal intothe cavity, wherein the volume of the projections is substantially equalto the volume of the ear, and an outline of the intermediate article issubstantially equal to the outline of the metal blank without the ear.2. The method of claim 1, wherein stamping the metal blank includesexerting a force in a predetermined direction, and the plastic flow ofthe portion of the metal is generally perpendicular to the predetermineddirection.
 3. The method of claim 1, further comprising pinch formingthe projection to create at least one guide.
 4. The method of claim 3,wherein pinch forming includes exerting a force in a predetermineddirection, and pinch forming results in an additional flow of a portionof the metal to form each guide with a predetermined height, the flowbeing plastic flow, and wherein the predetermined height is measuredgenerally perpendicular to the predetermined direction.
 5. The method ofclaim 3, wherein pinch forming includes shaving material located betweenthe two opposing surfaces, wherein the shaved material is directed toform at least a portion of the guide, and a shaved area is created. 6.The method of claim 5, wherein a thickness of the rocker arm, asmeasured between the shaved area and an opposing surface, is greaterthan a minimum required thickness.
 7. The method of claim 5, whereinpinch forming further includes directing the projections to form atleast a portion of the guide.
 8. The method of claim 3, wherein pinchforming further includes pinching a predetermined amount of materialbetween a pair of cams and a center post.
 9. The method of claim 1,wherein there are a pair of guides, and there is a separate ear for eachguide.
 10. A method of manufacturing a cam-engaged rocker comprising:obtaining a metal blank, the blank defined, at least in part, by anouter peripheral surface and two opposing surfaces, the blank having agenerally uniform thickness as measured between the two opposingsurfaces, wherein the two opposing surfaces each generally lie within adefined plane, the blank-further having a valve end and a pivot end,wherein the metal blank contains a predetermined amount of a metal; andstamping the metal blank by exerting a force on the metal blank througha stamping die having a cavity, wherein the stamping die is positionedadjacent the metal blank such that the cavity is adjacent one of the twoopposing surfaces at the valve end, and the cavity is adapted to permita portion of the blank to increase in thickness, such that a projectionis formed by the flow of the metal into the cavity, and wherein theforce is exerted through the outer peripheral surface.
 11. The method ofclaim 10, wherein stamping the metal blank includes exerting a force ina predetermined direction, and the flow of the metal is generallyperpendicular to the predetermined direction.
 12. The method of claim10, further comprising pinch forming the projection to create at leastone guide.
 13. The method of claim 12, wherein pinch forming includesexerting a force in a predetermined direction, and pinch forming resultsin an additional material thickness, wherein the additional materialthickness is measured generally perpendicular to the predetermineddirection.
 14. The method of claim 10, wherein pinch forming includesshaving material between the two opposing surfaces, wherein the shavedmaterial is directed to form at least a portion of the guide, and ashaved area is created.
 15. The method of claim 14, wherein a thicknessof the rocker arm, as measured between the shaved area and an opposingsurface, is greater than a minimum required thickness.
 16. The method ofclaim 14, wherein pinch forming further includes directing theprojections to form at least a portion of the valve guide.
 17. Themethod of claim 12, wherein pinch forming further includes pinching apredetermined amount of material between a cam and a center post.
 18. Amethod of manufacturing a cam-engaged rocker comprising: providing anarticle, the article defined, at least in part, by a body defined inpart by a first surface and an opposing second surface, the firstsurface having a projection that extends from the body, the articlefurther having a valve end and a pivot end, wherein the article containsa predetermined amount of a metal; and shaving a portion of the metalbetween the first surface and the opposing second surface to form aguide, wherein the guide is formed from metal that includes at least aportion of the projection, and the guide is defined at least by aninboard surface and an outboard surface.
 19. The method of claim 18,further comprising: stamping the article by exerting a force on themetal blank through a stamping die having a cavity, wherein the stampingdie is positioned adjacent the article such that the cavity is adjacentthe metallic surface at the valve end, and the cavity is adapted topermit a portion of the article to increase in thickness, such that theprojection is formed by the plastic flow of metal into the cavity, andwherein the force is exerted through an outer curved surface
 20. Anintermediate article of manufacture in the manufacture of a cam-engagedrocker arm having a guide, the article comprising: a metallic body,wherein the body is defined by two opposing surfaces and an outerperipheral surface disposed therebetween, wherein the body has athickness measured between the metallic surface and the opposingsurface, and the metallic surface defines at least one projection thatextends from the body; wherein the projection is selectively formed intothe guide.